Antenna decoupling by means of a lossy dielectric slab



Oct. 4, 1966 J. G. HOFFMAN 3,277,488

ANTENNA DECOUPLING BY MEANS OF A LOSSY DIELECTRIC SLAB Filed July 27,1964 JOHN G. HOFFMAN INVENTOR.

ATTORNEY United States Patent the Navy Filed July 27, 1964, Ser. No.385,525 5 Claims. ((11. 343-771) The invention herein described may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

The present invention relates to flush mounted antennas and moreparticularly to a means for reducing the coupling between flush mountedantennas in a common conducting ground plane.

. The coupling between flush mounted antennas (i.e. slots) has beenfound to be much different than with simple horn antennas, and alsoquite critical in terms of dielectric constant, dielectric loss tangentand thickness of the dielectric. The method of decoupling, used withhorn antennas, based upon absorbing the incident electric field of thefeed transmit horn is unsuccessful when used with flush mounted slotantennas. Old methods of obtaining decoupling in flush mounted slotantennas involved the use of chokes in the vicinity of the antennas, butthis had the detrimental effect of producing deterioration in theantennas radiation patterns.

The decoupling technique of the instant invention involves using a thinslab of dielectric mounted between flush mounted slot type receive andslot type transmit antennas to increase the surface impedance and todissipate the energy coupled into the dielectric.

It is an object of the invention to provide a means for reducing thecoupling between flush mounted antennas in a common ground plane.

Another object of the invention is to provide a decoupling means forflush mounted slot antennas by the use of a lossy dielectric slab.

A further object of the invention is to provide a high degree ofdecoupling between slot antenna arrays without causing deterioration inthe antennas radiation patterns.

Other objects and many of the attendant advantages of this inventionwill become readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing wherein:

The figure of drawing is a diagrammatic representation of a pair of slotantennas decoupled by means of a lossy dielectric mounted therebetweenon the surface of a cylindrical vehicle.

As shown in the figure of drawing, a transmit slottype antenna and areceive slot-type antenna 12 are mounted in a conducting cylindricalsurface 14 with a thin slab 16 of lossy dielectric mounted between thetwo antennas. The antennas may be mounted in either curved or flatconducting ground surfaces. The dielectric slab 16 can be mounted flushwith the antenna slots, or on either side of the conducting groundsurface 14.

The coupling mechanism between two slot antennas mounted in a conductingground plane is by means of a surface mode. It has been found that thedegree of coupling of this surface mode to the conducting surface isdependent upon the surface impedance of the ground plane. For a highlyconducting ground plane this mode is loosely coupled to the surface, andconsequently, any

obstructions in the ground plane will not cause appreciable decoupling:between the two antennas. Therefore, the purpose of this invention isto increase the surface impedance in order to couple the mode into thesurface very tightly and then dissipate the energy in the lossydielectric.

plane, and to dissipate the energy coupled into the dielectric.

A high degree of decoupling between slot antenna arrays is obtainable inthe instant case without causing deterioration in the antennas radiationpatterns by the lossy dielectric slab 16.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings.

practiced otherwise than as specifically described.

What is claimed is:

1. An antenna decoupling system for reducing the coupling between flushmounted slot-type antennas without producing deterioration in theantennas radiation patterms comprising:

(a) a common conducting ground plane, (b) a pair of longitudinalslot-type antennas flush mounted in said common conducting ground plane,

(c) a thin slab of lossy dielectric mounted on said common conductingground plane between said flush mounted antennas,

(d) said lossy dielectric slab increasing the surface impedance of theground plane between the anten- 4. A device as in claim 1 wherein anarray of flush mounted antennas are used.

5. A device as in claim 1 wherein said pair of longitudinal slot-typeantennas are parallel mounted.

References Cited by the Examiner UNITED STATES PATENTS 2,981,949 4/1961Elliott 343771 2,998,602. 10/1961 Cacheris 343782 HERMAN KARL SAALBACH,Primary Examiner.

ELI LIEBERMAN, R. HUNT, Assistant Examiners.

The lossy dielectric slab 16 has a two-fold V purpose: to increase thesurface impedance of the ground It is therefore to be understood thatwithin the scope of the appended claims the invention may be

1. AN ANTENNA DECOUPLING SYSTEM FOR REDUCING THE COUPLING BETWEEN FLUSHMOUNTED SLOT-TYPE ANTENNAS WITH OUT PRODUCING DETERIORATION IN THEANTENNAS'' RADIATION PATTERMS COMPRISING: (A) A COMMON CONDUCTING GROUNDPLANE, (B) A PAIR OF LONGITUDINAL SLOT-TYPE ANTENNAS FLUSH MOUNTED INSAID COMMON CONDUCTING GROUND PLANE, (C) A THIN SLAB OF LOSSY DIELECTRICMOUNTED ON SAID COMMON CONDUCTING GROUND PLANE BETWEEN SAID FLUSHMOUNTED ANTENNAS, (D) SAID LOSSY DIELECTRIC SLAB INCREASING THE SURFACEIMPEDANCE OF THE GROUND PLANE BETWEEN THE ANTENNAS AND DISSIPATINGENERGY COUPLED INTO THE DIELECTRIC.